compiz crashed with SIGSEGV in unity::ui::EdgeBarrierController::Impl::OnPointerBarrierEvent()

[Sparhawk]

This is what happened before the crash:
1) I connected another monitor to my laptop's mini-DVI port (which was previously set to span, not mirror).
2) Unity didn't recognise the monitor, so I opened up display settings.
3) The monitor was recognised, but then everything got slow temporarily.
4) In addition, the mouse cursor could move around the second monitor, but got "stuck" when it just entered the laptop's monitor.
5) I lost all window decorations, and couldn't alt-tab, etc. I was notified of a crash.
6) I had to switch to tty1 and run $ unity --replace . All was fine then.

This crash does not happen all the time.

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: unity 5.12-0ubuntu1.1
ProcVersionSignature: Ubuntu 3.2.0-25.40-generic 3.2.18
Uname: Linux 3.2.0-25-generic x86_64
ApportVersion: 2.0.1-0ubuntu8
Architecture: amd64
Date: Mon Jun 25 19:03:05 2012
Disassembly: => 0x0: Cannot access memory at address 0x0
ExecutablePath: /usr/bin/compiz
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
ProcCmdline: compiz --replace
SegvAnalysis:
 Segfault happened at: 0x0: Cannot access memory at address 0x0
 PC (0x00000000) not located in a known VMA region (needed executable region)!
SegvReason: executing NULL VMA
Signal: 11
SourcePackage: unity
StacktraceTop:
 ?? ()
 unity::ui::EdgeBarrierController::Impl::OnPointerBarrierEvent(unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent>) () from /usr/lib/compiz/libunityshell.so
 sigc::internal::slot_call2<sigc::bound_mem_functor2<void, unity::ui::EdgeBarrierController::Impl, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >, void, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >::call_it(sigc::internal::slot_rep*, unity::ui::PointerBarrierWrapper* const&, std::shared_ptr<unity::ui::BarrierEvent> const&) () from /usr/lib/compiz/libunityshell.so
 unity::ui::PointerBarrierWrapper::EmitCurrentData() () from /usr/lib/compiz/libunityshell.so
 ?? () from /usr/lib/compiz/libunityshell.so
Title: compiz crashed with SIGSEGV in unity::ui::EdgeBarrierController::Impl::OnPointerBarrierEvent()
UpgradeStatus: Upgraded to precise on 2012-04-29 (57 days ago)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare

[Apport retracing service (apport)]

StacktraceTop:
 ?? ()
 unity::ui::EdgeBarrierController::Impl::OnPointerBarrierEvent (this=0x2e61170, owner=0x3482220, event=...) at /build/buildd/unity-5.12/plugins/unityshell/src/EdgeBarrierController.cpp:139
 operator() (_A_a2=..., _A_a1=<optimized out>, this=<optimized out>) at /usr/include/sigc++-2.0/sigc++/functors/mem_fun.h:1917
 operator()<unity::ui::PointerBarrierWrapper* const&, const std::shared_ptr<unity::ui::BarrierEvent>&> (_A_arg2=..., _A_arg1=<optimized out>, this=<optimized out>) at /usr/include/sigc++-2.0/sigc++/adaptors/adaptor_trait.h:103
 sigc::internal::slot_call2<sigc::bound_mem_functor2<void, unity::ui::EdgeBarrierController::Impl, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >, void, unity::ui::PointerBarrierWrapper*, std::shared_ptr<unity::ui::BarrierEvent> >::call_it (rep=<optimized out>, a_1=<optimized out>, a_2=...) at /usr/include/sigc++-2.0/sigc++/functors/slot.h:173

[Daniel van Vugt (vanvugt)]

Looks like bug 983268. But that one is fixed already (!?).

[Sparhawk (sparhawkthesecond)]

Ah yeah, you are probably right. I did see that one suggested as a dupe, but it was not an outright dupe, just a launchpad suggestion.

(I also got confused, since AFAIK the HDMI out on my Dell laptop is hardwired differently to the mini-DVI out. e.g. it can only mirror, not span. Of course, there's no reason why mine is not dissimilar to other laptops.)